This invention relates to an improved synthetic fiber paper formed of a fibrous material, at least a part of which is composed of polyolefin fibers, and more particularly to a synthetic fiber paper having a good printability for offset printing. This invention also relates to methods for production of such improved synthetic fiber paper.
The sheet material formed of a fibrous material which is composed solely of polyolefin fibers or composed of a mixture of polyolefin fibers and natural cellulose fibers is advantageous in that it has a good water resistance, a chemical resistance and a dimensional stability, while it is disadvantageous for poor offset printability in comparison with a paper sheet formed solely of cellulose fibers.
As known to those skilled in the art, in the offset printing process it is impossible or extremely difficult to apply fountain solution and printing ink separately. It is also known that failure of transfer of printing ink is often caused due to poor absorption of fountain solution by the sheet to be printed thereon.
Generally, a pick resistance of the sheet formed of polyolefin fibers is not strong enough for offset printing because the internal bonding between polyolefin fibers in the sheet are not so strong. One of the effective methods for improving the pick resistance is to treat the sheet with an aqueous solution of adhesive in any of known manners such as tub sizing, surface sizing, coating, etc. However, application of the adhesive solution in an amount enough to obtain a good pick resistance prevents absorption of fountain solution with the result that transfer of printing ink to the paper surface is failed. This phenomenon is seen more remarkably as the polyolefin fiber content in the sheet is increased. Even with a sheet material containing polyolefin fibers in an amount of about 5% by weight with respect to that of cellulose fibers, so-called "snow flaking" is produced on the surface area where polyolefin fibers are exposed.
The primary object of this invention is to provide an improved synthetic fiber paper in which the above-mentioned disadvantages can be avoided. Particularly one of the objects of the invention is to provide a synthetic fiber paper formed of a fibrous material, at least a part of which is composed of polyolefin fibers, in which "pick resistance" and "offset printability" are improved.
Another object of this invention is to provide an economical and effective method for treatment to improve the printability of synthetic fiber paper formed of a fibrous material, at least a part of which is composed of polyolefin fibers.
Other objects and advantages of the invention will be partly apparent and partly discussed in detail hereinbelow.